Recently, with rapid improvement in performances and functions and rapid decrease in sizes and weights of electronic devices, electronic parts used in these electronic devices are required to have smaller sizes, lighter weights, and smaller thickness. Thus, on a print wiring board which is to be provided with electronic parts, it is required to install a semiconductor or the like in a high density manner, to make wires finer, and it is required to make the print wiring board multi-layered in order to reduce sizes and weights of the electronic parts and improve functions and performances of the electronic parts. In order to support finer wirings, it is necessary to use an insulative material having high electric insulation property for protecting the wirings. Further, as the print wiring substrate on which the electric parts are provided, a flexible print wiring board (referred to also as FPC as required) has recently attracted more attentions than an ordinary rigid print wiring board, and has come to be further demanded. Further, a resin is used as a material for various products such as an electric product, an automobile, and the like, due to its characteristics such as easiness to fabricate, mechanical property, electric property, appearance, and the like.
Incidentally, in producing the print wiring board, a photosensitive material is used in various manners. That is, the photosensitive material is used in (i) formation of circuit patterned on the print wiring board (pattern circuit), (ii) formation of a protection layer for protecting a surface and the pattern circuit of the print wiring board, (iii) formation of an insulation layer between layers in case where the print wiring board has a plurality of layers, (iv) and the like. As the photosensitive material used in these purposes, a liquid photosensitive material and a film photosensitive material are used. Among them, the film photosensitive material has such advantage that its film thickness is evener and its workability is more excellent than the liquid photosensitive material. Thus, various film photosensitive materials are used according to usages such as a pattern circuit resist film used to form a pattern circuit, a photosensitive cover lay film used to form the protection layer, a photosensitive dry film resist used to form the interlayer insulation layer, and the like.
For example, a polymer film referred to as a cover lay film is combined with a surface of the FPC so as to protect a conductive surface. As a process for combining the cover lay film with the conductor surface, it is general to perform the following process: The cover lay film, processed so as to have a predetermined shape, whose one side has an adhesive, is made to overlap the FPC and is properly positioned, and then the cover lay film is thermally pressed against the FPC with a pressing device or the like. However, as the foregoing adhesive, an epoxy adhesive or an acrylic adhesive is mainly used, but such adhesive is inferior in soldering heat resistance, bonding strength at high temperature, and flexibility. Thus, in case of combining the cover lay film with the conductor surface with an adhesive, it is impossible to sufficiently make use of a performance of the polyimide film.
Further, in case of combining the cover lay film with the FPC with the conventional epoxy adhesives or acrylic adhesives, it is necessary to form a hole or a window on an uncombined cover lay film so as to correspond to a junction of a terminal or a part of the circuit. However, the cover lay film is thin, so that it is difficult to form a hole and the like. Furthermore, the hole and the like of the cover lay film are almost manually positioned so as to correspond to junctions of terminals or portions of the FPC. This is not preferable in terms of workability and positional accuracy, and the manufacturing cost increases.
In order to improve the workability and the positional accuracy, conventionally, (i) a method for forming a protection layer by applying a photosensitive composition to the conductor surface and (ii) a photosensitive cover lay film (the photosensitive dry film resist is used as a cover lay film) have been developed, thereby improving the workability and the positional accuracy.
However, acrylic resins are used in the photosensitive cover lay film, so that its heat resistance property and durability of the film are not sufficient, and the film has no flame retardancy. That is, as the photosensitive cover lay film and the photosensitive dry film resist (hereinafter, both of them are generically referred to as a photosensitive dry film resist), merely acrylic or epoxy photosensitive dry film resists are focused at present, but there is such a problem that the film having been cured is inferior in heat resistance, chemical resistance, anti-bending property, and flame retardancy. In this way, the resin is more likely to burn than a metallic material or an inorganic material, so that improvement of the flame retardancy remains unrealized.
A general method for realizing the flame retardancy is a method in which a compound having a halogen is mixed. An example thereof is a photosensitive dry film resist produced by curing a photosensitive resin composition containing a bromic flame retardant (for example, Patent Document 1). However, the photosensitive dry film resist recited in Patent Document 1 contains the bromic flame retardant, so that the flame retardant having a halogen may have a bad influence on the environment. Further, the flame retardant having a halogen gives a great load to the environment, so that study on non-halogenous (halogen-free) materials is carried out all over the world. Thus, the halogen-free flame retardant is being studied instead of the bromic flame retardant (for example, Patent Documents 2, 3, and 4). As the halogen-free flame retardant, nitrogenous, phosphorus, and inorganic compounds, phosphate ester hydrate, red phosphorus hydrate, metal oxide hydrate, and the like, are known. However, phosphate ester and red phosphorus are hydrolyzed which may results in occurrence of phosphoric acid, and they are likely to drop electric reliability. The metal oxide scatters and absorbs light, so that it is difficult to use the metal oxide as the photosensitive resin.
Further, recently, a flame retardant using a resin to which a silicone compound has been added has been being studied (for example, Patent Document 5). Further, as a flame retardant, phosphazene compounds are being studied, and it is known that the phosphazene compounds exhibit high flame retardant effect (for example, Patent Document 7). Patent Document 7 discloses a flame retardant resin composition obtained by blending a phosphazene compounds with a polycarbonate resin and the like. The phosphazene compounds have an excellent effect in improving the flame retardancy, and has such an advantage that the phosphazene compounds give less load to the environment since this is a halogen-free flame retardant.
Further, conventionally, polyimide resin materials which can be bonded at low temperature and in short time and are superior in heat resistance have been proposed (for example, Patent Document 8). Further, as polyimide adhesive materials favorably used in production of the FPC, a material having photosensitivity has been proposed (for example, Patent Document 9). Also a laminate having not only flexibility but also heat resistance has been disclosed (for example, Patent Document 10). Incidentally, a resin material used in the wiring board is required to have flame retardancy as described above, and various kinds of resin materials whose flame retardancy has been improved are proposed (for example, Patent Document 11). Among them, it is more preferable to use a resin material having a phosphorus compound in order to avoid use of a material, giving some load to the environment, as much as possible.
[Patent Document 1]
Japanese Unexamined Patent Publication No. 335619/2001 (Tokukai 2001-335619)(Publication date: Dec. 4, 2001)
[Patent Document 2]
Japanese Unexamined Patent Publication No. 235001/2002 (Tokukai 2002-235001)(Publication date: Aug. 23, 2002)
[Patent Document 3]
Japanese Unexamined Patent Publication No. 19930/2001 (Tokukai 2001-19930)(Publication date: Jan. 23, 2001)
[Patent Document 4]
Japanese Unexamined Patent Publication No. 49090/2001 (Tokukai 2001-49090)(Publication date: Feb. 20, 2001)
[Patent Document 5]
Japanese Unexamined Patent Publication No. 40219/2001 (Tokukai 2001-40219)(Publication date: Feb. 13, 2001)
[Patent Document 6]
Japanese Unexamined Patent Publication No. 40149/2001 (Tokukai 2001-40149)(Publication date: Feb. 13, 2001)
[Patent Document 7]
Japanese Unexamined Patent Publication No. 181268/1999 (Tokukaihei 11-181268)(Publication date: Jul. 6, 1999)
[Patent Document 8]
Japanese Unexamined Patent Publication No. 242820/1995 (Tokukaihei 7-242820)(Publication date: Sep. 19, 1995)
[Patent Document 9]
Japanese Unexamined Patent Publication No. 27667/1994 (Tokukaihei 6-27667)(Publication date: Feb. 4, 1994)
[Patent Document 10]
Japanese Unexamined Patent Publication No. 733/1998 (Tokukaihei 10-733)(Publication date: Jan. 6, 1998)
[Patent Document 11]
Japanese Unexamined Patent Publication No. 335703/2001 (Tokukai 2001-335703)(Publication date: Dec. 4, 2001)
However, in case of using the nitrogenous compound, the phosphorus compound, or the inorganic compound as the halogen-free flame retardant, the nitrogenous compound generally has some influence on a curing property of the resin, and the phosphorus compound drops humidity resistance or has a similar influence, so that it is difficult to practically use each of these compounds. Thus, there are less choices of flame retardant materials which can be used in the photosensitive dry film resist required to have an electric insulation property and anti-hydrolysis property.
Further, also in case of using as the flame retardant the resin to which the silicone compound has been added, few kinds of resins can exhibit the flame retardant effect. Further, the flame retardant to which the silicone compound has been independently added rarely exhibits a great flame retardant effect, and even the flame retardant whose effect can be confirmed to some extent requires addition of a large quantity of silicone compounds in order to satisfy a strict flame retardant standard. As a result, a bad influence is exerted onto other necessary properties of the resin, so that this results in disadvantage in cost. Thus, use of such flame retardant is not practical.
Further, even in case of using the phosphazene compound as the flame retardant, when a resin obtained by mixing a conventional phosphazene compound is used in a cover lay film or the like, the phosphazene compound is deposited (bled or juiced) on a surface of the resin, so that properties of the resin drop. For example, conventionally used propoxylated phosphazene is in a liquid state, so that a bonding property of the photosensitive dry film resist cured after being treated at high temperature significantly drops.
Further, the resin is used for resin parts used in electric and electronic parts. In terms of environmental problems, solder containing no lead (lead-free solder) is practically used in a print wiring board on which the resin parts are installed. In case of using the lead-free solder, reflow temperature rises (250° C. to 260° C.), so that the resin parts are required to have sufficient heat resistance. However, in case of using the resin obtained by mixing the conventional phosphazene compound as the flame retardant, the phosphazene compound evaporates and disappears at such high temperature. Thus, a flame retardant which more persistently remains in the resin is required.
Further, a photo-curing resin which is cured by irradiation of an energy line such as an ultraviolet ray is practically used in various fields represented by a coating material field and an electric/electronic material field instead of a conventional thermosetting resin. As a compound which gives flame retardancy to the resin, an acrylic compound having a halogen and a compound having a double bond, e.g., a phosphate ester compound which is likely to be hydrolyzed, are known. However, each of these compounds has such a problem that this exerts a great load to the environment and such a problem that its hydrolysis property is low.
The present invention was made in view of the foregoing problems, and an object of the present invention is to provide (i) a phosphazene compound which allows water system development, formation of a favorable pattern shape, and realization of not only properties such as heat resistance, hydrolysis property, easiness to process (inclusive of solvent solubility), and bonding property, but also photosensitivity, flame retardancy, and sufficient mechanical strength, the phosphazene compound being favorably used to produce a wiring substrate for sufficiently supporting reduction of a size and a weight of each electronic part of an electronic device, and (ii) a photosensitive resin composition using the phosphazene compound, and (iii) typical usage thereof.